Just how bad can an Ion burn be?

[Eric H]

This bad.

Dumont 12JP4 installed in a Hoffman CT-800

Every 12JP4 I've had the misfortune of coming across has had this burn to some degree or another, this one is the worst.

It also had the worst emissions so probably a high hour tube, I cleaned it with the Beltron to get some brightness out of it, it really just made the spot look worse.
It's Green because it's a Hoffman.